Disk array devices making use of redundant array of inexpensive disks (RAID) technology are known, by way of example, as storage devices. In the disk array devices, redundant data is stored so as to be distributed across multiple hard disk drives (HDDs), and thus increased speed and fault tolerance may be securely achieved.
A disk array device includes, for example, multiple HDDs, and information representative of redundant data in the disk array device includes, for example, data and parity. Hereinafter, each HDD of a disk array device is sometimes referred to simply as a “disk”.
In the case where a disk in a disk array device fails, a rebuild process of restoring information in the failed disk by making use of data redundancy is performed. As techniques related to the rebuild process, for example, the following techniques are mentioned.
There is known a failure recovery method for recovering data of a failed drive by making use of a free area of a disk system (for example, refer to Japanese Laid-open Patent Publication No. 6-230903). In this failure recovery method, in a disk array device including a plurality of disk devices, error correction data for a collection of data to be written is generated from the collection of data, and the collection of write data and the error correction data are stored so as to be distributed over multiple disk devices. Data of a disk device that has failed is recovered from other data of the collection of write data and the error correction data stored on non-failed disk devices, and the recovered data is stored so as to be distributed across free areas of normal disk devices.
There is also known a disk array device with which, when a failure occurs in a magnetic disk, a delay in a data recovery process due to access loads of other magnetic disks is reduced (for example, refer to Japanese Laid-open Patent Publication No. 2005-38271). This disk array device has two kinds of parity data and a plurality of data recovery methods, and, in the case of a single magnetic disk failure, selects a data recovery method in which a magnetic disk that has degenerated and a magnetic disk with the largest load may be excluded for data recovery processing.
There is also known a disk array device that has a two-parity configuration and in which the parity and data of restoration sources are used on a rotation basis when read operations for error correction are carried out during a failure of one HDD (for example, refer to Japanese Laid-open Patent Publication No. 2006-260446).
In recent years, the capacities of disks have been increasing, and the time taken for restoring information of one disk through a rebuild process has increased significantly. For this reason, it is desired to increase the speed of the rebuild process.
However, in the case where, among a plurality of disks in which information areas that store information and spare areas are allocated, more disks than the number of spare areas fail, it is not easy to appropriately perform a rebuild process.
Such a problem arises not only in disk array devices using HDDs as storage devices but also in storage devices using other types of storage devices.